"Endearing the Line" Berlin-based artist Dirk Rathke has quickly built himself a reputation here in Houston. After several shows at Gallery Sonja Roesch, he's known for his curved canvases — monochrome shapes that bend, twist and seemingly ripple ever so slightly; you have to check the edge of the work just to make sure of their depth — and stripped-down drawings that go off the canvas entirely. In his third exhibition at the gallery, Rathke returns to familiar territory. As the name suggests, the show plays with line, space and dimension, resulting in playful, attention-holding pieces. The most prominent is the remarkable site-specific installation Room-drawing for Houston #2. In his first solo show at Sonja Roesch, back in 2007, Rathke memorably took over the back end of the gallery with neon orange tape. He does so again, this time placing orange tape in the shape of two squares that take over the ceiling, wall and floor. It's part sculpture, part painting, thanks to the brush stroke-like lines of the tape, and it completely throws you off. You're not sure how to react to it — do you look at it straight on, or dare to get inside the lines and challenge the 3-D quality of the work? The canvas-twisted works also play with this line between sculpture and painting. Rot Zweiteilig is the most striking of these, comprised of two solid-red canvases that are forced together, a line between them adding to the tension. In the future, it'd be nice to see the artist move in another direction instead of doing more of the same. But what he has now is still powerful, memorable work — those neon orange squares will be etched in my mind for quite some time. Through June 30. 2309 Caroline, 713-659-5424. — MD

"The Graphic Arts of Hans Erni" Hans Erni is one of Switzerland's best-known artists, and a contemporary of Picasso, Kandinsky and Mondrian. Over the decades, he's worked in lithography, digital technology and everything in between. At 103 years old, he still works in his studio every day, rivaling artists a quarter of his age. So I had high hopes for Erni's first major retrospective here in the United States, held at the Museum of Printing History. But I was let down. The retrospective consists of 40 posters, mainly painted illustrations, arranged for the most part in chronological order, from 1948 to 2009. In his decades-long career, Erni has done more than posters, and the museum's exhibition brochure even boasts that his work includes paintings, print and book illustrations, stage design, tapestry and postage stamps. Sure, the exhibition needs some focus given his wide span, but with row upon row of 128-by-91-centimeter posters, other types of graphic art would have been appreciated simply for some variety, as well as to accurately portray and pay tribute to the range of Erni's work. Another missing component is context. Given his Swiss pedigree, the posters are largely in French and German, and, removed from their time frame of reference, they're difficult to decipher. But you can still judge Erni's graphic artwork on its own. The work itself varies wonderfully in style and theme, from dramatic images of a skull topped with an atomic bomb plume to a decapitated tree (literally). Many are united by Erni's repeated use of geometric elements, especially circles, and sometimes even consistent fonts. In some works, the artist adopts styles similar to those of the masters, such as in a striking silkscreen from 1961 of a naked woman that's reminiscent of Picasso, and a Degas-esque print of a woman holding up a giant nut. These intriguing finds make for some standouts in this small show, which despite its flaws is necessary viewing for fans of Erni stateside. Through June 9. 1324 W. Clay St., 713-522-4652. — MD

"HJ Bott: Rhythm and Rhetoric" Houston artist HJ Bott has been exploring his so-called "displacement-of-volume system" for 40 years now, and he's celebrating with an exhibition of his newest works at Anya Tish Gallery. It says something that after 40 years, Bott hasn't gotten bored with his self-developed technique, which explores lines and geometric shapes on fiberboard that he then casts with glossy, bold color. And the op-art works themselves are far from boring — they're bright, colorful works that attract viewers like moths to a flame. And once they get you there, they're highly cerebral — through his sharp lines and shapes, Bott plays with dimension, creating 3-D shapes that almost seem to rotate in space on the canvas. It's no surprise that the boldest and the brightest of them all — Mesocarp Mischief — is the star of the show. The painting graces the cover of the latest Arts and Culture magazine, it's the poster image on the gallery's handout and it attracted gallery-goers during the opening like none of the other works. It's an intriguing visual — its thin black lines over the hot pink make it look like a Barbie barcode, while circles are uniquely dissected by lines, colors and curves. Bott says he's dabbling in concepts like yin/yang and string theory and applies layers of paint and glaze in vibrant colors up to 100 times, but his works lack emotion. It's all a bit too methodical — Bott even uses specific "warm" and "cool" colors to achieve the multi-dimensionality of his works. These works are all about dimension, but it's hard to get below the surface when it's all so manipulated. Through June 9. 4411 Montrose, 713-524-2299. – MD